The regulation of gene expression can occur at many levels. One aspect of gene expression that is poorly understood at this time is regulation at the level of selective translation of mRNA. The marine worm Urechis caupo is an ideal system for the study of this phenomenon, since dramatic changes occur in the translation of specific maternal mRNA, during oogenesis and fertilization. A large number of these mRNAs, have been identified and characterized using cDNA clones. I propose to focus on aspects of the structure of the different mRNAs to understand how their translation is regulated. This will be done by: 1) sequencing full- length cDNA clones complementary to maternal mRNAs translated at different times during oogenesis and fertilization in order to identify structures shared by mRNAs whose translation is regulated coordinately, and 2) injecting functional mRNAs synthesized in vitro into Urechis oocytes to compare the translation of wild-type mRNAs with molecules mutated in those regions likely to be involved in translation. Other experiments will investigate the role of polyadenylation in regulating translation and mRNA stability during oogenesis and embryogenesis, aspects of mRNA structure controlling the selective adenylations and deadenylations that occur at fertilization in Urechis, and the structure of mRNAs.